Embroidery frames, which usually comprise a closed inner frame and an outer frame, which is opened at one point, and have a clamping device, by means of which a clamping force suitable for the reliable fixation of the clamped workpiece can be set between the inner frame and the outer frame, are used to hold the workpiece to be processed for performing embroidery work on sewing machines and smaller embroidery machines. The clamping device comprises, in general, two projections, which project laterally at the ends of the outer frame, a threaded bolt fixed at one projection, and a threaded nut, which is screwed onto the said threaded bolt and is supported at the other projection.
In order not to exert an excessive bending moment on the ends of the outer frame by the threaded bolt arranged at a spaced location from the outer frame during the setting of the clamping force (this would lead to a deformation of the outer frame and consequently to a nonuniform distribution of the clamping force) it is sought that the distance between the threaded bolt and the outside of the outer frame be kept as small as possible. However, this possibility is limited by the fact that the threaded nut should have a shape and size as well as a position in relation to the outside of the frame which are favorable for grasping, because its diameter should not be too small for applying the necessary setting forces, and it should also possibly be located at a certain distance from the outside of the frame in order to be able to be grasped reliably.
This requirement can be met without any special problems in the case of round embroidery frames, because the free end of the threaded nut is located at an increasing distance from the circular outside of the outer frame with increasing length.
For rectangular embroidery frames, laid-open Japanese Patent Application JP-P Hei-2-264 059 suggests that the fastening device be arranged at one of the four corners of the frame, as a result of which the embroidery frame projects into the free space in a readily accessible manner. However, such an arrangement of the fastening device or of the point of separation of the outer frame is associated with the disadvantage of a very nonuniformly distributed clamping force between the outer frame and the inner frame.